I'm trying to build a query that extracts the input and output definitions for the functions in a schema. We've got multiple client types written in multiple languages, and plan to move many queries into stored functions. That way, each client can call a function without writing their own SQL code. I'd like to at least semi-automate the documentation, so I want to extract the inputs and outputs for each method. As an example, here's the sort of output I'm looking for from a sample method, listed below:

schema  function_name   lang    return_type run_as  owner_name  strict  returnset   volatile    comment is_input    item_number name    type    default
api push_log_count_since    plpgsql record  INVOKER user_bender f   t   v       t   1   since_dts   timestamptz 
api push_log_count_since    plpgsql record  INVOKER user_bender f   t   v       f   1   days_ago    int8    
api push_log_count_since    plpgsql record  INVOKER user_bender f   t   v       f   2   table_name  citext  
api push_log_count_since    plpgsql record  INVOKER user_bender f   t   v       f   3   server_name citext  
api push_log_count_since    plpgsql record  INVOKER user_bender f   t   v       f   4   push_count  int8    

The method has one input named since_dts and returns a table of results with four columns, as listed above and shown below:

CREATE OR REPLACE FUNCTION api.push_log_count_since (since_dts timestamptz)
        days_ago int8,
        table_name extensions.citext,
        server_name extensions.citext,
        push_count int8) 


-- Subtract two timestamptz values, get an interval, pull out just the days.
   days_ago bigint := date_part('day', now()::timestamptz - since_dts)::bigint;

    SELECT days_ago,
           ib_table_name as table_name,
           data_file_info.server_name_ as server_name,
           count(*) as push_count

      FROM ascendco.push_log
      JOIN ascendco.data_file_info on (data_file_info.id = push_log.data_file_id)

     WHERE push_log.push_dts >= since_dts

  GROUP BY ib_table_name,

  ORDER BY ib_table_name,
  COST 100
  ROWS 1000;

ALTER FUNCTION api.push_log_count_since (timestamptz) 
    OWNER TO user_bender;

I'm not wedded to my big flat output, and will likely convert the data to a JSON:

   "comment":"An COMMENT ON value set on the function.",

It looks like the data I need is in the pg_proc system catalog, but I'm not sure how to extract it in a way that I can readily use. I've been bashing away at this, and have gotten a lot closer than when I originally posted. The information_schema.parameters view makes things easier. This script is a bit involved, and I'd guess that there are much simpler ways to achieve the same results. I'd be grateful for any help or suggestions on how to improve this.

-- The script below takes a function's name+oid and returns a row for each input or output parameter.
-- Information about the routine overall is included on each row, such as schema, name, comments.
-- For each parameter, you get the absolute ordinal position, positin in the input/output list,
-- data type and default value. It's a bit of a Frankenscript, but it's getting close to what I'm after.
-- If I can get this working, I'll likely wrap it in a function.
WITH function_name_parts AS (
-- The information_shcema catalogs concatenate function_name + oid.
-- This provides a unique name for overloaded functions. Parse these bits out.          
  select * from string_to_array('push_log_count_since_329059','_') as parts

function_identity AS (
      -- Take the array from above and built up the combined name, name, and oid.
       -- ! There must be a simpler way to do all of this. 

        select array_to_string(parts,'_') AS function_name_and_oid,
                 array_to_string(array_remove_element(parts,cardinality(parts)),'_') AS function_name,
                parts[cardinality(parts)]::oid as function_oid

    from function_name_parts

-- Grab information from parameters and routines. I haven't figured out how to get the OWNER out of pg_proc.
-- The pg_get_userbyid(pg_proc.proowner) function seems like it should work, but I've not sorted out how to get that working.
SELECT parameters.specific_catalog AS database_name,
       row_number() OVER (partition by parameter_mode order by ordinal_position) as input_output_position,
       get_function_owner_name(function_oid) as owner_name, -- Is there a smarter way to do this than a custom function?
       obj_description(function_oid) AS comment

      FROM function_identity,
  LEFT JOIN information_schema.parameters  ON (information_schema.routines.specific_name = parameters.specific_name)

      WHERE parameters.specific_name = function_identity.function_name_and_oid

   ORDER BY ordinal_position

This returns output like the following:

database_name   function_name   function_oid    ordinal_position    input_output_position   parameter_mode  parameter_name  data_type   udt_name    parameter_default   external_language   security_type   owner_name  comment
squid   push_log_count_since    329059  1   1   IN  since_dts   timestamp with time zone    timestamptz NULL    PLPGSQL DEFINER user_bender NULL
squid   push_log_count_since    329059  2   1   OUT days_ago    bigint  int8    NULL    PLPGSQL DEFINER user_bender NULL
squid   push_log_count_since    329059  3   2   OUT table_name  USER-DEFINED    citext  NULL    PLPGSQL DEFINER user_bender NULL
squid   push_log_count_since    329059  4   3   OUT server_name USER-DEFINED    citext  NULL    PLPGSQL DEFINER user_bender NULL
squid   push_log_count_since    329059  5   4   OUT push_count  bigint  int8    NULL    PLPGSQL DEFINER user_bender NULL

The code for the array_remove_element function is here:

CREATE OR REPLACE FUNCTION tools.array_remove_element(anyarray, int)
'SELECT $1[:$2-1] || $1[$2+1:]';

COMMENT ON FUNCTION tools.array_remove_element(anyarray, int) IS '
From the ever-helpful Erwin Brandstetter, renamed for our schema and idiom.

ALTER FUNCTION tools.array_remove_element (anyarray, int) 
    OWNER TO user_bender;

The code for the get_function_owner_name function is found below:

CREATE OR REPLACE FUNCTION tools.get_function_owner_name(function_oid oid)
'select rolname::text from pg_authid where oid = (select pg_proc.proowner from pg_proc where oid = function_oid)';

ALTER FUNCTION tools.get_function_owner_name(function_oid oid) 
    OWNER TO user_bender;

1 Answer 1


This query will give you the argument types and result types as arrays for any function:

SELECT f.oid::regproc AS function_name,
       f.proargtypes::regtype[] AS argument_types,
       CASE WHEN f.proallargtypes IS NULL
            THEN ARRAY[f.prorettype::regtype]
            ELSE array_agg(args.type::regtype) FILTER (WHERE args.mode = 'o')
       END AS result_types
FROM pg_proc AS f
   LEFT JOIN LATERAL unnest(f.proallargtypes, f.proargmodes) AS args(type, mode)
      ON TRUE
GROUP BY f.oid, f.proallargtypes, f.prorettype, f.proargtypes;

Add a WHERE condition to restrict the output.

  • Thanks for the quick answer. The query above seems to return a packed element for the input, and null for the result types. I'm really trying to figure out how to split the inputs and outputs into individual rows or elements, if that makes sense. Commented Jan 23, 2020 at 23:53
  • 1
    Well, now you know where the data comes from; fitting it into the desired shape is left to the reader. Don't construct the array for result_types and unnest the argument types. Commented Jan 24, 2020 at 6:51

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